llvm/lib/LTO/Caching.cpp

   1 //===-Caching.cpp - LLVM Link Time Optimizer Cache Handling ---------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the Caching for ThinLTO.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/LTO/Caching.h"
  14 #include "llvm/ADT/StringExtras.h"
  15 #include "llvm/Support/Errc.h"
  16 #include "llvm/Support/FileSystem.h"
  17 #include "llvm/Support/MemoryBuffer.h"
  18 #include "llvm/Support/Path.h"
  19 #include "llvm/Support/Process.h"
  20 #include "llvm/Support/raw_ostream.h"
  21
  22 #if !defined(_MSC_VER) && !defined(__MINGW32__)
  23 #include <unistd.h>
  24 #else
  25 #include <io.h>
  26 #endif
  27
  28 using namespace llvm;
  29 using namespace llvm::lto;
  30
  31 Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
  32                                             AddBufferFn AddBuffer) {
  33   if (std::error_code EC = sys::fs::create_directories(CacheDirectoryPath))
  34     return errorCodeToError(EC);
  35
  36   return [=](unsigned Task, StringRef Key) -> AddStreamFn {
  37     // This choice of file name allows the cache to be pruned (see pruneCache()
  38     // in include/llvm/Support/CachePruning.h).
  39     SmallString<64> EntryPath;
  40     sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key);
  41     // First, see if we have a cache hit.
  42     SmallString<64> ResultPath;
  43     Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
  44         Twine(EntryPath), sys::fs::OF_UpdateAtime, &ResultPath);
  45     std::error_code EC;
  46     if (FDOrErr) {
  47       ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  48           MemoryBuffer::getOpenFile(*FDOrErr, EntryPath,
  49                                     /*FileSize=*/-1,
  50                                     /*RequiresNullTerminator=*/false);
  51       sys::fs::closeFile(*FDOrErr);
  52       if (MBOrErr) {
  53         AddBuffer(Task, std::move(*MBOrErr));
  54         return AddStreamFn();
  55       }
  56       EC = MBOrErr.getError();
  57     } else {
  58       EC = errorToErrorCode(FDOrErr.takeError());
  59     }
  60
  61     // On Windows we can fail to open a cache file with a permission denied
  62     // error. This generally means that another process has requested to delete
  63     // the file while it is still open, but it could also mean that another
  64     // process has opened the file without the sharing permissions we need.
  65     // Since the file is probably being deleted we handle it in the same way as
  66     // if the file did not exist at all.
  67     if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
  68       report_fatal_error(Twine("Failed to open cache file ") + EntryPath +
  69                          ": " + EC.message() + "\n");
  70
  71     // This native object stream is responsible for commiting the resulting
  72     // file to the cache and calling AddBuffer to add it to the link.
  73     struct CacheStream : NativeObjectStream {
  74       AddBufferFn AddBuffer;
  75       sys::fs::TempFile TempFile;
  76       std::string EntryPath;
  77       unsigned Task;
  78
  79       CacheStream(std::unique_ptr<raw_pwrite_stream> OS, AddBufferFn AddBuffer,
  80                   sys::fs::TempFile TempFile, std::string EntryPath,
  81                   unsigned Task)
  82           : NativeObjectStream(std::move(OS)), AddBuffer(std::move(AddBuffer)),
  83             TempFile(std::move(TempFile)), EntryPath(std::move(EntryPath)),
  84             Task(Task) {}
  85
  86       ~CacheStream() {
  87         // Make sure the stream is closed before committing it.
  88         OS.reset();
  89
  90         // Open the file first to avoid racing with a cache pruner.
  91         ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  92             MemoryBuffer::getOpenFile(
  93                 sys::fs::convertFDToNativeFile(TempFile.FD), TempFile.TmpName,
  94                 /*FileSize=*/-1, /*RequiresNullTerminator=*/false);
  95         if (!MBOrErr)
  96           report_fatal_error(Twine("Failed to open new cache file ") +
  97                              TempFile.TmpName + ": " +
  98                              MBOrErr.getError().message() + "\n");
  99
 100         // On POSIX systems, this will atomically replace the destination if
 101         // it already exists. We try to emulate this on Windows, but this may
 102         // fail with a permission denied error (for example, if the destination
 103         // is currently opened by another process that does not give us the
 104         // sharing permissions we need). Since the existing file should be
 105         // semantically equivalent to the one we are trying to write, we give
 106         // AddBuffer a copy of the bytes we wrote in that case. We do this
 107         // instead of just using the existing file, because the pruner might
 108         // delete the file before we get a chance to use it.
 109         Error E = TempFile.keep(EntryPath);
 110         E = handleErrors(std::move(E), [&](const ECError &E) -> Error {
 111           std::error_code EC = E.convertToErrorCode();
 112           if (EC != errc::permission_denied)
 113             return errorCodeToError(EC);
 114
 115           auto MBCopy = MemoryBuffer::getMemBufferCopy((*MBOrErr)->getBuffer(),
 116                                                        EntryPath);
 117           MBOrErr = std::move(MBCopy);
 118
 119           // FIXME: should we consume the discard error?
 120           consumeError(TempFile.discard());
 121
 122           return Error::success();
 123         });
 124
 125         if (E)
 126           report_fatal_error(Twine("Failed to rename temporary file ") +
 127                              TempFile.TmpName + " to " + EntryPath + ": " +
 128                              toString(std::move(E)) + "\n");
 129
 130         AddBuffer(Task, std::move(*MBOrErr));
 131       }
 132     };
 133
 134     return [=](size_t Task) -> std::unique_ptr<NativeObjectStream> {
 135       // Write to a temporary to avoid race condition
 136       SmallString<64> TempFilenameModel;
 137       sys::path::append(TempFilenameModel, CacheDirectoryPath, "Thin-%%%%%%.tmp.o");
 138       Expected<sys::fs::TempFile> Temp = sys::fs::TempFile::create(
 139           TempFilenameModel, sys::fs::owner_read | sys::fs::owner_write);
 140       if (!Temp) {
 141         errs() << "Error: " << toString(Temp.takeError()) << "\n";
 142         report_fatal_error("ThinLTO: Can't get a temporary file");
 143       }
 144
 145       // This CacheStream will move the temporary file into the cache when done.
 146       return std::make_unique<CacheStream>(
 147           std::make_unique<raw_fd_ostream>(Temp->FD, /* ShouldClose */ false),
 148           AddBuffer, std::move(*Temp), std::string(EntryPath.str()), Task);
 149     };
 150   };
 151 }